In a copending application of Norman L. Stauffer, Ser. No. 912,688, filed June 5, 1978, now U.S. Pat. No. 4,185,191, issued Jan. 22, 1980 a range determination system is shown which is useable in a through-the-lens camera for positioning the taking lens at a desired correct focus position with respect to a remote object within the field of view. That system utilizes a plurality of small detectors such as charge coupled devices (CCD) or charge injection devices (CID) mounted in an array to receive radiation from the scene being viewed. The detectors are arranged in pairs with each pair being mounted behind a small lenslet so that each pair receives a view of the exit pupil of the taking lens but one of the detectors in each pair receives radiation primarily from a first portion of the taking lens while the other of the detectors in each pair receives radiation primarily from a different portion of the taking lens. The result is to create two similar curves indicative of the radiation distribution pattern from the scene being viewed. At the proper focus position, the two curves coincide, but as the object changes position with respect to the camera, the two curves move with respect to each other to indicate an out-of-focus situation. The two curves move with respect to each other in a first direction when the object moves closer to the camera than the desired focus position and move in an opposite direction with respect to each other as the object moves further from the camera than the desired focus position. By determining the direction of movement of the two curves with respect to each other, it is therefore possible to determine the direction that the taking lens has to be moved to achieve the desired focus position.
In a copending application of Norman L. Stauffer and Dennis J. Wilwerding, Ser. No. 016,595, filed Mar. 1, 1979, now U.S. Pat. No. 4,249,073 an improvement on the above-mentioned copending application Ser. No. 912,688 is disclosed wherein a method and apparatus for determining the direction in which the two similar curves should be moved in order to produce the coincidence indicative of a proper focus position. In that application, a value indicative of the slope of the curves at predetermined points is obtained and this value is multiplied by the difference in the value of the output of the detectors at such points. The product is summed over a predetermined range. The summation value is substantially 0 when the two curves coincide but will have a characteristic such as plus or minus to indicate the direction the taking lens must be moved when the two curves do not coincide.
In a copending application of Dennis J. Wilwerding and James D. Joseph, Ser. No. 058,964, filed July 20, 1979, now U.S. Pat. No. 4,250,376 an improvement on the above-mentioned copending applications is disclosed wherein the need for taking the product of the value indicative of the slope of the curves and the value indicative of the difference is eliminated and in lieu thereof a first signal representative of the absolute magnitude of the difference between the outputs of the two detectors, one from each of the curves, is produced and a second signal representative of the absolute magnitude of the difference between the outputs of two other detectors, one from each of the curves, is also produced. The two absolute magnitude signals are differenced and the result is summed over a predetermined range. The resultant summed signal is substantially 0 when the two curves coincide, will have a first characteristic such as a negative sign when the two curves are displaced in the first direction and a second characteristic such as a positive sign when the two curves are displaced in the opposite direction so as to provide the desired direction signal.
In a copending application of Norman L. Stauffer and Dennis J. Wilwerding, Ser. No. 074,845, filed Sept. 13, 1979, now U.S. Pat. No. 4,254,330 an improvement on the above-mentioned systems is disclosed which operates to prevent a false 0 cross-over situation that can occur in highly repetitive patterns and which produces a summation signal that responds to the low frequency variations in the pattern.
All of the above copending applications involve circuitry for use in highly accurate auto focus systems for use on fairly expensive cameras such as single lens reflex types and accordingly the relatively high cost of the auto focus systems is not of serious consequence. There is a need, however, for a low cost auto focus system that may be useable in less expensive cameras and still retain most of the advantages obtained from the above-mentioned copending applications.